JPH0982345A - Fused carbonate fuel cell and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance corrosion resistance of a wet sealing part. SOLUTION: In a wet sealing part, an aluminium diffused layer 111 is formed on a surface of a base material 55 which contains aluminium of 1 to 9wt.% and is composed of alloy mainly composed of iron. The wet sealing part is manufactured by forming the aluminium diffused layer by performing heat treatment after coating the surface of the base material which contains aluminium of 1 to 9wt.% and is composed of alloy mainly composed of iron with aluminium. The wet sealing part is manufactured by forming the aluminium diffused layer on the surface of the base material by soaking the base material which contains aluminium of 1 to 9wt.% and is composed of alloy mainly composed of iron in a molten aluminium bath.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molten carbonate fuel cell, and more particularly to improving the corrosion resistance of the wet seal portion to prolong the life and improve the performance.

[0002]

2. Description of the Related Art Generally, a unit cell is composed of a fuel electrode, an electrolyte matrix and an oxidizer electrode. A porous sintered body of transition metal such as nickel is used for the fuel electrode,
As the oxidizer electrode, an oxide porous body of nickel or the like having high electron conductivity is used as in the fuel electrode. Also,
The electrolyte matrix is used by impregnating a sintered body of lithium aluminate particles with an electrolyte. A binary system of lithium and potassium carbonate is mainly used as the electrolyte, and the composition ratio of these is high ionic conductivity, and the melting point must be lower than 650 ° C. which is the operating temperature of the battery. A carbonate is used which has a composition or a composition close to that of the composition. In particular, lithium and potassium carbonate are advantageous and widely used from the viewpoint of the electrode reaction rate of the oxidizer electrode. Molten carbonate fuel cells that are put to practical use are generally
An electrolyte matrix is sandwiched between a fuel electrode and an oxidizer electrode, and they are stacked to form a single cell. A plurality of stainless / nickel thin plates called separator plates and a single cell are sequentially stacked in series.

As a fuel gas of a molten carbonate fuel cell, methane gas and steam or hydrogen or carbon dioxide, which is steam reformed from methane using a reformer, is supplied as a main component, and oxygen is used as an oxidizer gas. Gases containing nitrogen and carbon dioxide are used. The chemical species involved in the electrode reaction at the fuel electrode are hydrogen, carbon dioxide and water vapor. The thermodynamic physical properties of the gas differ depending on the composition ratio,
The higher the hydrogen concentration in the fuel gas, the higher the cell characteristics.

FIG. 4 shows an example of a unit cell having an internal manifold type structure of a molten carbonate fuel cell using an alkali metal carbonate whose electrolyte becomes a liquid at 650 ° C. proposed in Japanese Patent Laid-Open No. 2-75162. FIG. 6 is a perspective view of a main part with a part thereof broken away, and FIG. 5 is a perspective view of a main part of the unit cell enlarged. In each figure, 10 is a separator plate,
Reference numerals 1 and 5 are a fuel electrode and an oxidizer electrode, which are separately installed by a separator plate 10. Reference numerals 3 and 7 are a fuel-side corrugated plate and an oxidant-side corrugated plate, which form a fuel gas passage and an oxidant gas passage provided between the separator plate 10 and the fuel electrode 1 and the oxidant electrode 5. Reference numeral 4 is an electrolyte matrix which is installed between the fuel electrode 1 and the oxidizer electrode 5 and constitutes a single cell. Reference numerals 2 and 6 denote a fuel-side perforated plate and an oxidant-side perforated plate that hold the fuel electrode 1 and the oxidizer electrode 5 and allow the generated current to pass therethrough, but they are omitted in FIG. 4 for simplicity. Reference numerals 20 and 30 are manifolds for supplying and exhausting the fuel gas and the oxidant gas. Reference numerals 21 and 31 denote wet seal portions provided on the fuel gas side surface and the oxidant gas side surface of the separator plate 10 around the electrodes 1 and 5 and the manifolds 20 and 30, respectively, to separately seal the inside and outside of the cell and the inside and outside of the manifolds 20 and 30. . Reference numeral 41 denotes an end spacer, which is an end member made of the same material as the fuel electrode 1 or the oxidizer electrode 5, and the fuel side corrugated plate 3 or the oxidizer side, as described in JP-A-63-28977. Corrugated board 7
And are overlapped with each other and are inserted inside the wet seal portions 21 and 31. Reference numeral 13 denotes an end member of the end spacer 41 on the oxidant electrode 5 side. The arrow 22 indicates the flow of fuel gas, and the arrow 32 indicates the flow of oxidant gas.

FIG. 6 is a perspective view showing a state where the wet seal portions 21 and 31 are attached to both surfaces of one separator plate 10, respectively. In the figure, the wet seal portion 2 is shown.
40 indicated by diagonal lines on the outer periphery of 1, 31 respectively
Is a welded portion for joining with the separator plate 10.

On the other hand, FIG. 7A shows the wet seal portion 2
FIG. 2 is an enlarged view of a cross section of a main part showing a state in which aluminum is thermally sprayed on the surfaces of 1, 31. In the figure, 50 is a base material of a wet seal part, 103 is an aluminum sprayed layer, and 104 is a part of aluminum to which aluminum is not attached. The thermal spray defect portion 105 is a void portion. FIG. 7B is an enlarged view of a cross section of a main part showing a state in which aluminum is diffused on the surface of the base material 50 of the wet seal part by performing heat treatment after the aluminum is sprayed, and 106 is an aluminum diffusion layer in the figure. , 107 is the aluminum spray defect portion 1
An aluminum non-diffusion defective portion existing at a position corresponding to 04 is a corroded portion 109 generated inside the wet seal portion base material 50 from the aluminum non-diffusion defective portion 107.

Wet seal portions 21 located around both ends of the fuel electrode 1 and the fuel gas supply / exhaust manifold 20, or both ends of the oxidant electrode 5 and the oxidant gas supply / exhaust manifold 30.
The wet seal portion 31 located around the fuel cell is kept in a wet state with the electrolyte by being brought into contact with the matrix 4 that holds the electrolyte, and by applying a constant surface pressure, the fuel gas in the cell or Prevent the oxidant gas from leaking to the outside of the battery and the manifold 20, 30 or vice versa.
It is configured for the purpose of not being mixed in. Therefore, the vicinity of the wet seal parts 21 and 31 in the battery operating state is always in contact with the high temperature electrolyte of about 650 ° C., and is in a severe corrosive environment in which a local battery reaction is likely to occur due to a potential difference or the like. As the material of the wet seal portions 21 and 31, for example, corrosion-resistant stainless steel such as SUS316L or SUS310S is used.
Under such a severe environment, there is a problem in long-term corrosion resistance. Therefore, as a countermeasure, as shown in FIG. 7, aluminum is first sprayed on the surface of the base material 50 of the wet seal portions 21 and 31 to form the aluminum sprayed layer 103 having a maximum thickness of 100 μm or more and 150 μm or less. After that, a heat treatment is performed at 900 ° C. for 1 hour in a reducing gas atmosphere (for example, an argon gas atmosphere) to form the aluminum diffusion layer 106 on the surface of the base material 50 of the wet seal portion, thereby providing corrosion resistance. .

[0008]

The wet seal portion of the conventional molten carbonate fuel cell, particularly the wet seal portion, is constructed and manufactured as described above. For example, in the above aluminum spraying method, aluminum is easily oxidized. When the sprayed aluminum adheres to the surface of the base material 50 of the wet seal part, the fusion between the aluminum particles is poor, the aluminum sprayed layer 103 becomes very uneven, and the defective part 104 where no aluminum is adhered at all is formed. And voids 105 are scattered. When the defect portion 104 and the void 105 are large, even if heat treatment is performed to diffuse aluminum on the surface of the base material 50 of the wet seal portion, an undiffused portion 107 in which a diffusion layer is not formed is generated in that portion. Therefore, corrosion 109 is generated from the non-diffused portion 107, so that the corrosion resistance treatment effect cannot be obtained, and there is a problem that battery life is impaired. It should be noted that the thick aluminum spray layer 103 can eliminate defects, but the thicker the aluminum spray layer 103, the thicker the aluminum diffusion layer 10 is.
6 had a problem such as cracking. As described above, since the wet seal part is placed in a severe corrosive environment, it is difficult to maintain the corrosion resistance for a long time, and a structure and a manufacturing method having more excellent corrosion resistance are required.

An object of the present invention is to solve the above problems and to obtain a molten carbonate fuel cell having excellent corrosion resistance and long life.

[0010]

In a molten carbonate fuel cell according to claim 1 of the present invention, the wet seal part has
An aluminum diffusion layer is formed on the surface of a base material made of an alloy containing 9% by weight of aluminum and containing iron as a main component.

In the method for manufacturing a molten carbonate fuel cell according to claim 2 of the present invention, the wet seal portion is formed on the surface of a base material made of an alloy containing 1 to 9% by weight of aluminum and containing iron as a main component. It is manufactured by coating aluminum followed by heat treatment to form an aluminum diffusion layer.

According to a third aspect of the present invention, in the method for producing a molten carbonate fuel cell, the heat treatment according to the second aspect is a step of joining a base material of a wet seal portion whose surface is coated with aluminum and a separator plate. A step of laminating a plurality of carbon spacers inserted in the space between the wet seal portion and the separator plate and the electrode insertion space via a carbon patch plate, and both ends of the laminate with a metal plate via the carbon patch plate. It is sandwiched by pressing plates made of the above and is heated in a state where the laminated body is pressurized.

According to a fourth aspect of the present invention, there is provided a method for manufacturing a molten carbonate fuel cell, wherein the wet seal portion comprises a base material made of an alloy containing 1 to 9% by weight of aluminum and having iron as a main component. It is manufactured by immersing in a bath to form an aluminum diffusion layer on the surface of the base material.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1. The first embodiment of the present invention will be described below. As an example of an alloy containing 1 to 9% by weight of aluminum and containing iron as a main component, which is used as a base material of a wet seal portion according to the present invention, two types of aluminum-containing ferritic stainless steels and conventionally have been applied. Thermogravimetric analysis was performed to compare the corrosion resistance of two austenitic stainless steels. FIG. 1 shows heating conditions and analysis results. In the figure, the vertical axis of the graph represents weight change (or temperature) and the horizontal axis represents time. Of the analysis curves,
The broken line and the alternate long and short dash line are the austenitic stainless steels SUS316L and SUS310S which have been conventionally applied.
And the solid line is 18Cr-3Al (abbreviation) of the aluminum-containing ferritic stainless steel according to the present invention,
20Cr-5Al (abbreviation) also became a curve almost overlapping with the curve of 18Cr-3Al. Table 1 shows the main components of the two types of aluminum-containing ferritic stainless steels according to the present invention, which are commercially available heat-resistant and corrosion-resistant materials manufactured by Sumitomo Metal Industries, Ltd.

[0015]

[Table 1]

Next, the method and results of the thermogravimetric analysis will be described. 53 mol% of lithium carbonate and 47 mol of sodium carbonate are placed on the entire surface of the sample having a thickness of 0.5 mm and a size of 1 cm square.
A eutectic salt consisting of mol% was mixed with the same amount of ethanol to form a slurry, and the slurry was applied.
It was made to become. The analytical conditions are a mixed gas atmosphere of 70 mol% of air and 30 mol% of carbon dioxide, and the curve 10 in FIG.
As shown by 0, the heating rate is 5 ° C / ° C from 0 ° C to 200 ° C.
Min., 200 ° C. to 650 ° C. was 0.7 ° C./min, and analysis was carried out in the state of holding at 650 ° C. for 40 hours. As a result, while the weight gains of the materials of SUS316L and SUS310S which have been conventionally applied are clearly shown, 18C of the aluminum-containing ferritic stainless steel according to the present invention is shown.
r-3Al and 20Cr-5Al are almost unchanged.
That is, it is clear from this analysis result that the aluminum-containing ferritic stainless steel according to the present invention is superior in corrosion resistance to conventional materials.

The corrosion resistance of the materials was evaluated by a method of immersing in a molten carbonate in addition to the thermogravimetric analysis method described above.
The test method is 62 mol% lithium carbonate and 38 potassium carbonate.
Each sample was immersed in a high-purity alumina crucible containing a mol% eutectic salt, and a test was performed at a temperature of 700 ° C. under an air atmosphere for 3000 hours. As a result of observing the surface and the cross section after the test, the austenitic stainless steels SUS316L and SUS310S were significantly corroded, while the aluminum-containing ferritic stainless steels 18Cr-3Al and 20Cr-5Al had an alumina coating on the surface. Almost no corrosion is caused by the formation, and the results of this immersion test show that the aluminum-containing ferritic stainless steel according to the present invention is superior in corrosion resistance to conventional materials. However, aluminum-containing ferritic stainless steel did not cause remarkable corrosion as in austenitic stainless steel, but pitting was observed. Therefore,
Although the corrosion resistance of aluminum-containing ferritic stainless steel is superior to that of conventional materials, it is not appropriate to use the material alone.

2 and 3 illustrate a molten carbonate fuel cell according to Embodiment 1 of the present invention and a method for manufacturing the same, and FIG. 2 (a) shows aluminum on the surface of the base material of the wet seal portion. FIG. 2B is an enlarged cross-sectional view of an essential part showing a coated state, and FIG. 2B is a cross-sectional view of the essential part schematically showing a state where aluminum is diffused on the surface of the base material of the wet seal part after the above aluminum coating. Is. In the figure, 55 is a ferritic stainless steel 18Cr-3Al or 20Cr- containing 3% by weight of the main components shown in Table 1 and 5% by weight of aluminum.
The base material of the wet seal portion made of 5Al, 110 is a defect-free aluminum coating layer formed by applying aluminum paint, and 111 is an aluminum diffusion layer having no defect and a uniform thickness. FIG. 3 shows the wet seal parts 21, 31 using a tightening jig when performing the heat treatment.
6A and 6B show a state in which a plurality of integrated structures of the separator plate 10 and the separator plate 10 are stacked and constrained under pressure, and 60a is a carbon spacer inserted in the gap between the wet seal parts 21 and 31 and the separator plate 10, Reference numeral 60b is a carbon spacer placed in the electrode insertion area, 62 is a carbon contact plate contacting the surfaces of the upper and lower wet seal portions 21, 31, and 64 is a carbon contactor with the carbon spacers 60a, 60b inserted therein. A pressing plate made of stainless steel that abuts on the upper and lower surfaces of the laminated body laminated with a plate 62 via the carbon contact plate 62, and 66, 67, 68, 69 are tightening for pressing and restraining the laminated body. Parts, screw rod, nut,
Spring washers and plain washers.

Next, a method of forming the aluminum coating layer 110 will be described. First, on the surface of the base material 55 of the wet-sealed portion that has been subjected to sandblasting, aluminum powder having an average particle size of 10 μm or less is 54.5% by weight or more and 58.5% by weight or less, and methylcellulose is used as a binding agent 3. 0% by weight or more and 7.0% by weight or less, phosphoric acid 7.0% by weight or more and 9.0% by weight or less, chromium trioxide 3.0% by weight, water 26.5% by weight, respectively mixed and stirred. Spray paint with aluminum paint consisting of The thickness of the aluminum coating layer 110 is 50 μm from the surface of the base material 55 of the wet seal portions 21 and 31.
The range is 150 μm or less. Because 150
If the thickness is more than μm, cracks may occur in the coating film at the stage of drying and firing, and also the possibility that cracks may occur in the aluminum diffusion layer 111 after heat treatment,
This is because when the thickness is 50 μm or less, the thickness of the aluminum diffusion layer 111 becomes small and the processing effect cannot be obtained.

After applying the aluminum paint, first, it is dried at room temperature for 1 hour, then at 80 ° C. for 1 hour or more, and at 300 ° C. for 3 hours.
The coating was cured by baking for 0 minutes or more to make it stable. If the coating is not sufficiently dried, cracking may occur in the coating during firing, or voids may occur inside the coating, making it impossible to form a stable coating, so it is necessary to dry it sufficiently. is there. After the aluminum coating layer 110 is formed by the above method, heat treatment is performed to form the aluminum diffusion layer 1 on the surface of the base material 55 of the wet seal portion.
11 was formed. The heat treatment in this case was performed by the following method in order to prevent thermal strain of the wet seal portions 21 and 31 and the separator plate 10.

In the present embodiment, the wet seal portion 21,
Aluminium-containing ferritic stainless steel is used as the base material 55 of 31, and austenitic stainless steel is used for the separator plate 10 to weld them to form an integrated structure. In this case, thermal distortion occurs when heat treatment is performed at a high temperature because the thermal expansion coefficients of the two are different. Therefore, it is necessary to take measures to prevent distortion when performing heat treatment, and the following methods have been devised as measures against them. First, a carbon spacer 60a having a thickness corresponding to the gap dimension between the wet seal portions 21 and 31 and the separator plate 10 is inserted, and the wet seal 21 is inserted into the electrode insertion spaces on both sides of the separator plate 10. , 31 and the separator plate 10 with a carbon spacer 60b having a thickness corresponding to the gap dimension between them,
A plurality of layers are laminated via a carbon plate 62, and both ends, that is, the upper and lower surfaces of the laminated body are sandwiched by a carbon pressing plate 62 and a stainless steel pressing plate 64, and a screw rod 66, a nut 67, and a spring washer 6
8. The flat washer 69 was fastened with a constant surface pressure by the tightening parts to restrain the pressure. The tightening force in this case is 6
The initial deformation of 8 was crushed completely and flattened. It should be noted that the contact plate 6 to be brought into contact with the wet seal surface
The reason why the material of No. 2 is carbon is as follows.
For example, when a metal plate is used as the contact plate 62, the aluminum coated on the wet seal surface during the heat treatment diffuses also to the metal surface side of the contact plate 62, and aluminum diffusion to the wet seal surface becomes insufficient. In addition, the wet seal surface and the contact plate 62 are fixed to each other and cannot be decomposed after the heat treatment. Then, as a result of conducting an experiment using a carbon plate as the backing plate 62, it was confirmed that the above-mentioned problems did not occur and the carbon plate was suitable.

Heat treatment was carried out in this manner to diffuse aluminum on the surface of the base material 55 for the wet seal portion.
The heat treatment conditions in this case were 900 ° C. and 1 hour in a hydrogen atmosphere. As a result, a uniform aluminum diffusion layer 111 having no defects could be formed.

In this way, the wet seal parts 21, 3
A battery assembled in the same configuration as the conventional example was used for 1 and aluminum was subjected to aluminum diffusion treatment, and it was operated for 10,000 hours under the same conditions as the conventional example.
There was no deterioration in battery characteristics due to corrosion of No. 31, and a stable battery could be obtained. Further, as a result of the disassembly examination, it was observed that the base materials were partially corroded in the conventional example as to the corrosion of the wet seal parts 21 and 31, but in the present example, such a part was not observed at all. It was confirmed that the effect of improving the corrosion resistance was great. In addition to the evaluation of corrosion resistance during battery operation, evaluation was also performed by a method of immersing in molten carbonate. The test method was the same as that of the material test described above, and the test was performed for 3000 hours. As a result, no occurrence of corrosion was observed, a sound aluminum diffusion layer was maintained, and it was proved that the corrosion resistance was higher than that of the conventional one.

In the above embodiment, the pre-firing and firing temperature after applying the aluminum paint are constant, and
The heat treatment was performed under a constant heat treatment condition, but the pre-firing temperature was in the range of 70 ° C to 90 ° C and the firing temperature was 3 ° C.
The temperature may be set in the range of 00 ° C. to 350 ° C., the heat treatment atmosphere may be Ar or vacuum, the heat treatment temperature may be set in the range of 850 ° C. to 900 ° C., and the time may be set in the range of 1 hour to 2 hours. It was possible to form an aluminum diffusion layer having a uniform thickness and no defects, as in the first embodiment. However, since the thickness of the aluminum diffusion layer 111 depends on the heat treatment temperature and time, the thickness of the aluminum diffusion layer 111 becomes thicker when the time is lengthened at a high temperature, and becomes smaller when the time is short at a low temperature. Further, if the thickness of the aluminum diffusion layer 111 is about 100 μm or more, cracks may occur in the diffusion layer, and if it is too thin, corrosion resistance cannot be obtained. Therefore, regarding the combination of the temperature and time of the heat treatment, it is necessary to lengthen the time when processing is performed at a low temperature in the above temperature range, and conversely, it is necessary to shorten the time when processing at a high temperature. For example, when the temperature is 850 ° C, the time is 2 hours and 875 ° C.
If this is set, the time should be about 1.5 hours.

Embodiment 2 Hereinafter, with respect to the second embodiment of the present invention, materials other than the materials described in the first embodiment will be described as the base material of the wet seal portion. In the first embodiment, two types of 18Cr-3Al and 20Cr-5Al materials have been described as examples of the corrosion resistance evaluation results of aluminum-containing ferritic stainless steels. However, other than this, aluminum-containing ferritic stainless steels having different aluminum content ratios have been described. The corrosion resistance of stainless steel and workability such as weldability were evaluated. Table 2 shows the evaluation results of materials containing aluminum and chromium as the main constituents with different content ratios. In the table, ○ indicates good, Δ indicates slightly bad, and X indicates defective. It is a representation.

[0026]

[Table 2]

Next, the result will be described. First, in terms of corrosion resistance, a ferritic stainless steel containing no aluminum, for example, SUS430, does not provide sufficient corrosion resistance under the environment of this type of battery, but the corrosion resistance of aluminum by about 1% by weight The improvement effect of was obtained. However, as described above, the aluminum-containing ferritic stainless steel did not cause remarkable corrosion unlike austenitic stainless steel, but small pitting corrosion was observed. The amount of pitting corrosion tended to decrease as the aluminum content increased, and pitting did not occur when the aluminum content was about 10% by weight. in this way,
It was confirmed that the corrosion resistance increases as the aluminum content increases. However, on the other hand, in terms of workability, especially weldability, there is a high possibility that problems such as cracking in the weld will occur as the aluminum content increases, and aluminum content of about 10% by weight In such cases, phenomena such as cracking and poor penetration were remarkably observed. Therefore, the optimum value of the aluminum content ratio that satisfies both corrosion resistance and workability is preferably in the range of 1% by weight or more and 9% by weight or less.

A ferritic stainless steel having an aluminum content ratio in the range of 1% by weight or more and 9% by weight or less as described above is applied to the base material 55 of the wet seal portion, and the same surface as in the first embodiment is obtained. The aluminum diffusion layer 111 was formed on the surface by the treatment method, and a battery assembled in the same configuration as the conventional one was operated under the same conditions as the conventional one for the same time. It was possible to obtain a stable battery. Further, as a result of the disassembly examination after the operation, it was confirmed that the wet seal portion had no corrosion that would affect the battery characteristics, and the corrosion resistance was superior to the conventional one. In addition to the evaluation in battery operation, an immersion test in molten carbonate was also conducted by the same method as in Embodiment 1, but no corrosion occurred, and this evaluation result also shows that it is better than the conventional one. It was confirmed that the product has excellent corrosion resistance.

In the above-described first and second embodiments, ferritic stainless steel is given as an alloy containing aluminum and having iron as a main component, but the present invention is not limited to this. For example, nickel less than 6% by weight and chromium 13 Even in an iron-based alloy containing less than wt%, the same effect of improving corrosion resistance can be obtained if it contains 1 to 9 wt% of aluminum.

Embodiment 3 A third embodiment of the present invention will be described. In the first embodiment, the wet seal portion 2
Although a method of coating aluminum paint on the surface of the base material 55 of Nos. 1 and 31 has been described, aluminum vapor deposition or aluminum plating may be performed as another method.
A uniform aluminum coating layer 110 without defects is obtained. Therefore, after the aluminum coating layer 110 is formed by these methods, the same heat treatment as that described in the first embodiment is performed, whereby a uniform aluminum diffusion layer 111 having no defects on the surface of the base material 55 of the wet seal portion is formed. Thus, the same effect as that of the first embodiment can be obtained.

Embodiment 4 FIG. Hereinafter, the fourth embodiment of the present invention will be described. In this embodiment, the wet seal part base material 55 is formed by the molten aluminum bath dipping treatment method.
Diffusing aluminum on the surface of. The molten aluminum bath immersion treatment method is a method of immersing the wet seal portion base material 55 in the molten aluminum bath to directly form the aluminum diffusion layer 111 on the surface of the base material 55, and the first embodiment
The aluminum diffusion layer 1 can be formed in one step without the need of two treatment steps such as aluminum coating treatment and heat treatment.
Since 11 can be formed and heat treatment is not required, the processing cost and the processing step can be saved, so that the cost can be reduced and the processing time can be shortened. However, generally, the thickness of the formed aluminum diffusion layer 111 can be made larger in the case of the first embodiment. In this embodiment, the aluminum-containing ferritic stainless steel shown in the first embodiment is applied to the base material 55 of the wet seal portions 21 and 31, and the aluminum diffusion layer 111 is formed on the surface of the base material 55 by the molten aluminum bath dipping treatment. It was made. The thickness of the aluminum diffusion layer 111 in this treatment is preferably in the range of 20 μm or more and 80 μm or less. This is because if the thickness is 80 μm or more, the aluminum diffusion layer 111 is more likely to crack, and if it is less than 20 μm, the treatment effect cannot be obtained. As described above, in this embodiment, the processing steps can be shortened as compared with the case of the first embodiment, but
Although it is difficult to obtain a thick aluminum diffusion layer 111, since the aluminum-containing base material 55 is used in the present invention, sufficient corrosion resistance can be obtained even if the thickness of the aluminum diffusion layer 111 is thinner than that of the conventional one.

The method of immersion treatment in the molten aluminum bath is described in the literature (Journal of the Japan Society for Marine Engines, Vol. 21, No. 9, p. 70-75).
) And the like, first, the wet seal base material 55 is subjected to pretreatment such as acid cleaning, water cleaning, and drying, and then immersed in a molten aluminum bath at a temperature of 700 ° C. and held for about 1 hour. After that, it was taken out from the molten aluminum bath and subjected to post-treatments such as acid washing, water washing and drying. In this case, in order to increase the thickness of the aluminum diffusion layer 111,
Immersion time is about 1 hour and this type of standard treatment time is 2
It was longer than 0 to 30 minutes. As a result, a uniform aluminum diffusion layer 111 without defects could be formed.

In this way, the wet seal parts 21, 3 to which the aluminum-containing ferritic stainless steel is applied
A battery assembled in the same configuration as the conventional one was used for 1 and was operated for 10,000 hours under the same conditions as the conventional one. However, the deterioration of the battery characteristics due to the corrosion of the wet seal parts 21 and 31 did not occur. It was possible to obtain a stable battery. Further, as a result of the disassembly examination after the operation, it was confirmed that the wet seal portion had no corrosion that would affect the battery characteristics, and the corrosion resistance was superior to the conventional one. Separately from the evaluation in battery operation, an immersion test in a molten carbonate was carried out by the same method as in Embodiment 1, but no corrosion occurred, and this evaluation result also showed that the corrosion resistance was better than that of the conventional one. Was confirmed to be excellent.

In the above embodiment, the immersion time in the molten aluminum bath is set to 1 hour, but it may be set in the range of 30 minutes or more and 1.5 hours or less, and the same effect as that of the above embodiment can be obtained. To be

[0035]

As described above, in the molten carbonate fuel cell according to the invention of claim 1, the wet seal portion has 1 to 9 parts.
Since the aluminum diffusion layer is formed on the surface of the base material made of an alloy containing iron by weight and containing aluminum by weight, sufficient corrosion resistance can be obtained.

In the method for manufacturing a molten carbonate fuel cell according to the second aspect of the present invention, the wet seal portion has a content of 1 to 9% by weight.
Since it is manufactured by coating aluminum on the surface of a base material made of an alloy containing aluminum as a main component and then subjecting it to heat treatment to form an aluminum diffusion layer, it is possible to impart sufficient corrosion resistance to the wet seal part. .

In the method for producing a molten carbonate fuel cell according to claim 3 of the present invention, the heat treatment according to claim 2 is a step of joining a base material of a wet seal portion whose surface is coated with aluminum and a separator plate. A step of laminating a plurality of carbon spacers inserted in the space between the wet seal portion and the separator plate and the electrode insertion space via a carbon patch plate, and both ends of the laminate with a metal plate via the carbon patch plate. Since it has a step of heating the laminated body by sandwiching it with a pressing plate made of, it is possible to prevent the occurrence of thermal strain during heat treatment even if the materials of the base material and the separator plate are different and the coefficients of thermal expansion are different. .

In a method for manufacturing a molten carbonate fuel cell according to a fourth aspect of the present invention, the wet seal portion is a molten aluminum containing a base material made of an alloy containing 1 to 9% by weight of aluminum and having iron as a main component. Since it is manufactured by immersing it in a bath and forming an aluminum diffusion layer on the surface of the base material, sufficient corrosion resistance can be imparted to the wet seal portion.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing an example of evaluating the corrosion resistance of a wet seal member according to a first embodiment of the present invention and a conventional material.

FIG. 2 relates to the first embodiment of the present invention, (a) shows a state in which aluminum paint is applied to the surface of the wet seal portion, and (b) shows a state in which aluminum is diffused after applying the aluminum paint in (a). It is a principal part sectional view which each shows typically.

FIG. 3 is a sectional view of relevant parts for explaining the heat treatment method according to the first embodiment of the present invention.

FIG. 4 is a partially cutaway perspective view showing a structure of a general unit cell of a conventional molten carbonate fuel cell of an internal manifold type.

FIG. 5 is a perspective view of an essential part showing a part of FIG. 4 in an enlarged manner.

FIG. 6 is a main part perspective view showing a general structure of a separator plate of a conventional molten carbonate fuel cell of an internal manifold type, partially broken away.

FIG. 7 relates to a conventional molten carbonate fuel cell,
(A) is an enlarged cross-sectional view of a main part schematically showing a state where aluminum is sprayed on the surface of the wet seal portion, and (b) is a state where aluminum is diffused after aluminum spraying of (a).

[Explanation of symbols]

1 fuel electrode, 4 matrix, 5 oxidant electrode, 10
Separator plate, 20 fuel side manifold, 21 fuel side wet seal part, 30 oxidant side manifold,
31 oxidizer side wet seal part, 40 weld part, 55
Aluminum-containing ferritic stainless steel base material, 60a, 6
0b carbon spacer, 62 carbon patch plate, 64
Holding plate, 66 screw rod, 67 nut, 68 spring washer, 69 flat washer, 103 aluminum sprayed layer, 10
6 Aluminum diffusion layer, 110 Aluminum paint layer, 111 Defect-free aluminum diffusion layer.

Claims (4)

[Claims] 1. A stack formed by alternately stacking a single cell having a fuel electrode, an electrolyte matrix, and an oxidant electrode, and a separator plate forming a gas flow path, for supplying and exhausting a fuel and an oxidant gas. In a molten carbonate fuel cell comprising an internal manifold and a wet seal part provided around the electrodes and the manifold in contact with the separator plate, the wet seal part is 1 to 9% by weight.
2. A molten carbonate fuel cell, characterized in that an aluminum diffusion layer is formed on the surface of a base material made of an alloy containing aluminum as a main component containing aluminum. 2. A stack formed by alternately stacking a single cell having a fuel electrode, an electrolyte matrix, and an oxidant electrode, and a separator plate forming a gas flow path, for supplying and exhausting a fuel and an oxidant gas. In a method of manufacturing a molten carbonate fuel cell comprising an internal manifold and a wet seal part provided around the electrodes and the manifold in contact with the separator plate, the wet seal part contains 1 to 9% by weight of aluminum. A method for producing a molten carbonate fuel cell, which is produced by coating a surface of a base material made of an alloy containing iron as a main component with aluminum and then performing heat treatment to form an aluminum diffusion layer. 3. The heat treatment according to claim 2, wherein a step of joining a base material of a wet seal portion whose surface is coated with aluminum and a separator plate, a space between the wet seal portion and the separator plate, and an electrode insertion space. A step of stacking a plurality of carbon spacers inserted through a carbon backing plate, and a state in which both ends of the above-mentioned laminated body are sandwiched by pressing plates made of metal through the carbon backing plate and the above-mentioned laminated body is pressed. The method for producing a molten carbonate fuel cell according to claim 2, which has a step of heating. 4. A stack formed by alternately stacking a single cell having a fuel electrode, an electrolyte matrix, and an oxidant electrode and a separator plate forming a gas flow path, for supplying and exhausting a fuel and an oxidant gas. In a method of manufacturing a molten carbonate fuel cell comprising an internal manifold and a wet seal part provided around the electrodes and the manifold in contact with the separator plate, the wet seal part contains 1 to 9% by weight of aluminum. Manufacture of a molten carbonate fuel cell, which is manufactured by immersing a base material made of an alloy containing iron as a main component in a molten aluminum bath to form an aluminum diffusion layer on the surface of the base material. Method.